1. Field of the Invention
The present invention relates to capacitive extensometers.
2. Description of the Prior Art
Extensometers are commonly used for measuring strain in a specimen and includes devices which utilize two arms held together by suitable cross flexure members as shown in U.S. Pat. No. 3,789,508. Strain gages applied to the cross flexure members are used for determining arm separation, and thus, specimen strain.
Capacitive sensing extensometers are known as well, but generally they are complex in operation, hard to adjust, and are not rugged and easily attached to the specimens.
A capacitive crack opening displacement gauge is shown in U.S. Pat. No. 4,098,000. This device has the sensing units on an opposite side of the hinge axis or pivot axis from the specimen engaging members, and uses differential capacitive sensing plates.
A capacitive reactance gauge probe, or proximity probe that employs the principles of a probe used with the present invention is shown in U.S. Pat. No. 3,400,331, but does not show any specific uses in connection with extensometers.
Likewise, U.S. Pat. No. 3,206,970 shows a capacitor that has two cylindrical members, the gap between which is measured by capacitive sensing, and which cylindrical members are moved as a function of the movement being sensed. Direct spacing change between two capacitor plates is thus used for sensing in this device.